> Open/closed source is a LICENSE, not a methodology for the style to write code.

You are right. However when you write open source code, you know by definition that you potentially expose it to public developers, among whom there are competent people. Sometimes they are even more competent than you, so you tend to write it as clean as you can. Obviously, it does not mean your code is not error-prone. By the way, "as clean as you can" is quite subjective and does not always mean "clean"